Various encapsulation techniques have been described in the art as a manner for protecting and delivering cosmetic/pharmaceutical actives. In particular, there is widespread interest to encapsulate sunscreen actives to ensure their protection in a formulated product, and to minimize skin penetration upon application. A significant problem with current sunscreens is their potential interaction in a formulated product leading to a reduction of their UV absorbance activity. One way to prevent the interactions is to isolate the sunscreen by encapsulating one or more sunscreen agent and composition thereof. Representative examples of microcapsules containing UV sunscreens are disclosed in FR2 642 329, DE-A 195 37 415, EP-A 509 904, FR 2 726 760 and FR 2 687 914 as well as WO 00/71084, U.S. Pat. No. 6,303,149, WO 98/31333, U.S. Pat. No. 5,876,699 and WO 00/72806.
JP-A-2-2867 describes sunscreen benzophenone derivatives encapsulated in fine spherical silica particles. The sunscreen is dissolved in aqueous alkali metal silicate solution and is emulsified in an organic non-solvent to form a water-in-oil emulsion. The emulsion is acidified to form a water-insoluble precipitate of sunscreen encapsulated in silica. The process of JP-A-2-2867 is suitable for hydrophilic sunscreen active materials, but most sunscreen active materials are lipophilic.
WO-A-98/31333 describes sunscreen-doped sol-gel materials and a method for their preparation comprising condensation polymerising a metal or semi-metal alkoxide or ester in the presence of at least one sunscreen ingredient, resulting in the entrapment of the sunscreen ingredients within the formed sol-gel matrix.
U.S. Pat. No. 6,303,149 describes a process for preparing sol-gel microcapsules loaded with functional molecules by emulsifying sol-gel precursors and the functional molecules in an aqueous solution, and mixing the emulsion with an acidic, neutral or basic aqueous solution to obtain a suspension of microcapsules. This sol-gel process described is a multiple kettle process requiring removal of the continuous phase.
U.S. Pat. No. 6,238,650 describes a sunscreen composition comprising at least one sunscreen active ingredient and a cosmetically acceptable vehicle, wherein said sunscreen active ingredient is in the form of sol-gel microcapsules containing at least one sunscreen compound. The sol-gel microcapsules are prepared by the method disclosed in U.S. Pat. No. 6,303,149.
EP-A-281034 describes a perfume encapsulated and/or clathrated in a matrix of inorganic polymer prepared from a metal alkoxide such as tetraethyl orthosilicate (TEOS). An aqueous dispersion or solution of perfume and TEOS is treated with an acid catalyst to cause hydrolysis, then with a base catalyst to cause polymerisation to a gel.
EP-A-941761 describes a process for preparing microcapsules with an organopolysiloxane shell and a core material, in which the shell is formed in situ by hydrolysis and polycondensation of an organosilane and/or a condensation product thereof having at most 4 silicon atoms.
JP-51-78995-A describes dispersing a silyl-treated pigment with TEOS in acetone and adding to ammoniacal aqueous ethanol with stirring to form a micropowder of particles having a pigment core.
EP-A-934773 describes microcapsules whose capsule wall comprises organopolysiloxane synthesised by polycondensing a compound of the formula RnSi(OH)mY(4-m-n) where m=1-4; n=0-3; R represents an organic group with a C atom directly bonded to a SI atom; and Y is an alkoxy group, H or a siloxy group.
WO-A-00/71084 describes preparing a sunscreen composition with improved photostability that contains at least two sunscreen actives which are photo-unstable when formulated together by microencapsulating at least one of the actives and adding other components of the sunscreen composition.
WO-A-01/80823 describes a therapeutic or cosmetic composition comprising microcapsules of diameter 0.1-100μ having a core-shell structure. The core includes at least one active. The shell comprises an inorganic polymer obtained by a sol-gel process, and releases the active after topical application.
WO-A-03/066209 describes a process of making lipophilic cosmetic, chemical, or pharmaceutical active material compositions encapsulated within a shell obtained from the emulsion polymerisation products of tetraalkoxysilane. The process of making these microcapsules is a one kettle process without removal of the continuous phase.
WO-A-2005/009604 describes a process of making core-shell microcapsules wherein the shell comprises at least one inorganic polymer comprising polymerized precursors obtained by in-situ polymerization of the precursors; wherein the concentration of the core material based total weight of the microcapsules is above 95% w/w.
WO-A-03/066209 describes a new encapsulation process by ex-situ emulsion polymerization from tetraalkoxysilanes and the surfactant concentration in the starting cationic emulsion.
There is a need for encapsulated sunscreens in a form in which the encapsulating shell is sufficiently robust to prevent leakage of the sunscreen into the formulation composition where antagonistic effects can occur. Furthermore, it is desirable to prevent skin contact and penetration of the sunscreen. The problem of leakage is particularly severe with cinnamic ester derivatives such as 2-ethylhexyl methoxycinnamate also known as EHMC or OMC or Parsol® MCX. EHMC is known to be a useful UV B absorber but that compound can cause unwanted effects, e.g. allergic reactions, and they have also a significant cross-reactivity with other sunscreen agents in particular with butylmethoxydibenzoylmethane.
The present inventors have discovered an improved process for preparing microcapsules using an “ex-situ emulsion polymerization” of tetraalkoxysilanes. In particular, the present inventors have discovered the combination of two process parameters during ex-situ emulsion polymerization results in the production of microcapsules having improved formulation integrity and performance. These parameters involve controlling the amount of cationic surfactant present in the process and the overall shell thickness of the micro capsule.